The cytokine interleukin-10 (IL-10) is a dimer that becomes biologically inactive upon disruption of the non-covalent interactions connecting its two monomer subunits. IL-10 was first identified as a product of the type 2 helper T cell and later shown to be produced by other cell types including B cells and macrophages. It also inhibits the synthesis of several cytokines produced from type 1 helper T cells, such as γ-interferon, IL-2, and tumor necrosis factor-α (TNF-α). The ability of IL-10 to inhibit cell-mediated immune response modulators and suppress antigen-presenting cell-dependent T cell responses demonstrates IL-10 has immunosuppressive properties. This cytokine also inhibits monocyte/macrophage production of other cytokines such as IL-1, IL-6, IL-8, granulocyte-macrophage colony-stimulating factor (GM-CSF), granulocyte colony-stimulating factor (G-CSF), and TNF-α. As a result of its pleiotropic activity, IL-10 is under investigation for numerous clinical applications, such as for treating inflammatory conditions, bacterial sepsis, enterotoxin-induced lethal shock, and autoimmune diseases, e.g., rheumatoid arthritis, allograft rejection and diabetes.
IL-10 has a relatively short serum half-life in the body. For example, the half-life in mice as measured by in vitro bioassay or by efficacy in the septic shock model system [see Smith et al., Cellular immunology 173:207-214 (1996)] is about 2 to 6 hours. A loss of IL-10 activity may be due to several factors, including renal clearance, proteolytic degradation and monomerization in the blood stream.
Pegylation of a protein can increase its serum half-life by retarding renal clearance, since the PEG moiety adds considerable hydrodynamic radius to the protein. However, the conventional pegylation methodologies are directed to monomeric proteins and larger, disulfide bonded complexes, e.g., monoclonal antibodies. Pegylation of IL-10 presents problems not encountered with other pegylated proteins known in the art, since the IL-10 dimer is held together by non-covalent interactions. Dissociation of IL-10, which may be enhanced during pegylation, will result in pegylated IL-10 monomers (PEG-IL-10 monomers). The PEG-IL-10 monomers do not retain biological activity of IL-10. It is also noted that di-PEG-IL-10, i.e., pegylation on two amino acids residues of IL-10, does not retain significant in vitro biological activity.
It would be an advantage to have an IL-10 product that is better able to tolerate systemic exposure during treatment, by enhancing the circulating life (delayed clearance), solubility and stability of IL-10, without disrupting the dimeric structure and affecting the activity of IL-10. The present invention addresses this and other related needs in the art.